1. Field of Disclosure
This disclosure relates generally to acoustic pulse recognition for sensing and localizing touches on a surface, and more specifically to using keys to limit contact areas on the surface for generating an acoustic signal.
2. Description of the Related Art
Acoustic pulse recognition (APR) determines the location of a touch on a surface by detecting and processing acoustic signals generated as a result of the touch. Acoustic signals of different wave patterns are generated when different parts of the surface are touched. Hence, by analysing an acoustic signal generated in response to a touch of the surface, the location of the touch can be determined. One way of analysing the acoustic signal includes storing reference acoustic signals generated in response to touching multiple reference points of the surface during a calibration stage, and then comparing the stored reference acoustic signal with an acoustic signal generated in response to touching of an unspecified location of the surface during an operational stage. Extrapolation or interpolation may be made based on the reference acoustic signals to approximate the unspecified location of the touch at the touch associated with the generated acoustic signal.
There are several ways to improve the accuracy of the localization in APR. One way is to increase the number of sensors for detecting the acoustic signal. By using more acoustic signals, ambiguity on the touched location can be reduced. Specifically, some geometric configuration of the touched surface may cause the same or a similar acoustic signal to be detected at a sensor even when different locations of the surface are touched. But another sensor placed in a different location or in a different orientation may detect distinct acoustic signals under such circumstances. Hence, adding sensors may resolve the issue associated with touches on different locations causing the same acoustic signal. Another way of increasing the accuracy is to increase the number of reference points and corresponding number of reference acoustic signals stored for comparison in the operation stage. However, such increased number of sensors or reference points leads to increased cost and processing requirements.
Moreover, these solutions do not completely eliminate the ambiguity associated with acoustic signals generated, especially, when a touch is made around border areas of each region of the surface associated with a different input value. Assume, for example, that two regions of the surface associated with two different input values are adjacent to each other. If a user touches the border area of the two regions, the acoustic pulse generated in response may cause random selection between the two input values, which may not always reflect the user's intended choice of input. Such unintended input in conjunction with the lack of tactile feedback may exacerbate user experience associated with a user input device using APR.